Knife blades for power shears are an example of this type of attachment. A power shears is conventionally provided with knife blades of elongate prismatic shape and with a rectangular cross section, there being an upper movable blade and a lower fixed blade. The long sides of the rectangle are normally substantially longer than its short sides, and the blade is placed in its holder with the long side of the rectangle upright. The lower holder is formed by the shears table, and the upper holder by a vertically movable beam incorporated in the shears. The lower short side of the lower blade abuts against a support surface on the table which takes up the vertical shearing force. A wide side of the blade is pressed against a vertical support surface of the table by a plurality of screws distributed along the length of the blade. In a corresponding mode, the upper blade is attached to the beam in the opposite position, an upper short side thus abutting an upward support surface of the beam.
This type of attachment is functionally satisfactory and the structure is simple. However, it is burdened with certain disadvantages which have made themselves more and more apparent in conjunction with the increased production rate of modern power shears.
A modern high-production power shears can have a cutting length of 5 to 10 meters, and work at a rate of 10 to 30 strokes per minute. Even with currently available high-quality material in the knife blade, this results in relatively rapid wear of the blade, so that it must be exchanged. Changing conventionally attached blades is a time-consuming procedure however, since a large number of attachment screws must be undone before the worn blade can be removed. It is also necessary to get at the shears from the back, between its end frames. For this purpose, it may be necessary to first of all dismantle the adjustable plate stops and conveyor means provided for handling the cut plates or sheets. Handling the blades, especially the upper blades, also affords certain problems since the relatively heavy objects must be lifted and transported manually within limited space.